The charged particle microscope is widely used for observing the structure of substances at a high magnification. However, drift can sometimes occur due to the characteristics of the specimen and the equipment stage. Charged particle microscopes generally shift the imaging field of view by moving a stage carrying a specimen placed on a sampling stage. However, due to problems with mechanical precision, the stage does not suddenly stop even if stop operation was initiated and still continues to moves even though only a small distance. Drift is caused mainly by the slight movement of the sampling stage after stop operation.
In the charged particle microscope, the capture of the image for observation requires a long time ranging from a few seconds to several dozen seconds and moreover is imaging that is enlarged to a high magnification so that even just a slight amount of drift causes distortion to appear in the image. However, finding what extent of image displacement has occurred due to drift, or finding in what direction the displacement amount occurred, just in the image where distortion occurred was impossible (in the related art) so preventing distortion from entering the image at the time of measurement or some type of method for correcting distortion in the image is needed.
One way to prevent distortion from entering an image during measurement, is to start the observation after waiting for the sampling stage to come to a complete stop after operation to stop the sampling stage movement however the image capture efficiency in that case is extremely poor. In order to resolve the problem, a variety of methods to correct image distortion due to drift were contrived.
The patent literature 1 for example discloses a drift correction method to correct slow-scan images by utilizing results from finding the drift amount (drift speed) per unit of time in the X direction and the Y direction from two fast-scan images (television scanning image) in order to find the displacement amount, due to drift in the image captured by slow-scan.